docs: def prepare_gold(ctx, annotations, gout):
      """Prepare bc-evaluate gold file from annotations supplied by CHEMDNER."""
      click.echo('chemdataextractor.chemdner.prepare_gold')
      for line in annotations:
          pmid, ta, start, end, text, category = line.strip().split('\t')
          gout.write('%s\t%s:%s:%s\n' % (pmid, ta, start, end))